I have a couple brass Granzow diaphram (sprinkler style) valves lying around. One is a 1 inch pipe thread and one is 1 and 1/4 inch thread. I am considering building a 1/2 inch aluminum barrel gun with the 1 inch valve. This will keep the CV up beyond what is "Needed" for a 1/2 inch cannon. This will be an all metal cannon that will be running a minimum of 300 psi.

What I am curious from you guys is this;

Should I build a cool assault looking rifle with decent performance, or ignore the cool factor and push for the highest possible performance (super long barrel, high tank/barrel ratio, crazy high FPS)?

This will still be a hand-held rifle. But, I am leaning toward making a couple different barrels and tanks that can easily be interchanged. I already have all the materials on-hand. The grip, pilot valve, and trigger will all be mounted to the vavle. That way the tank and barrel will be super easy to change and it will be easy to disassemble for service, and easy transport.

Hmm, It would be cool to make a super long barrel. Like 10 foot or more and see what kind of velocity I can achieve. I bet super-sonic would be possible with 300 PSI and a 7 or 8 gram light weight plastic slug.

Anyway, I am so used to making stuff that just looks cool. However, I really want something that will impress. It is tough to make a small bore cannon do much damage. I think this is a worthy challenge. Besides, I already own everything I need to do this.

High-PSI wrote:or ignore the cool factor and push for the highest possible performance (super long barrel, high tank/barrel ratio, crazy high FPS)?

Build a hybrid

IMO, small bore, high pressure pneumatics get pretty boring pretty fast, especially if they are just one-shots. Use the valves to pilot a much larger valve, like a 4" piston valve

I know, I know. My 2 inch cannon is a blast (pun intended). It disintigrates 4 inch concrete cinder blocks. It kicks the shoulder enough to border on painful, is impressive to look at, and is super loud! But, I think it is cool to have something that does not weigh 35 pounds and take 3 minutes to charge the tank.

Oh, also, I can always have a 1 inch barrel on-hand for some larger projectiles. It is, after all, a 1 inch valve........

Hmm, I have that 1 and 1/4 inch valve too. I should build two cannons while I am at it. I am very familiar with these valves and the particulars related to welding the tank together and everthing else. So, this should not take too much time to build.

I have a basic 3 foot long barrel .6" bore cannon built (I have no pictures of it yet). I used my 1 inch bore brass diaphram valve pilotted by a 1/2 inch diaphram valve triggered by a small air trigger valve I picked up from McMaster. The tank is a .1 inch thick steel affare welded together. The tank is 3 inch diameter, 5 inches long. I have fired it a few times with pressures ranging from 200 to 300 PSI. It is loud, I can tell you that. It is, also, very powerful for a small bore cannon. I fired it through a few sheets of aluminum plate I had lying around. I need to fire it into some plywood sheets to see how much penetration power it has. All I have left is the grip and a simple shoulder stock to make. Oh, I have a 6 foot barrel for it too. It should freakin ROCK with that long barrel! But, it would be weird to carry around with such a long barrel.

Oh, my compressor can charge the cannon to 100 PSI in 5 seconds, 200 PSI in 12 seconds and 300 psi in about 25 seconds. Much better than waiting 3 minutes to charge like my big cannon. Of course, the big cannon is much more impressive to fire.

At any rate, I am pleased enough with this cannon that I am going to take my time making the grip and stock.

Hey, one interesting observation, I innitially installed the trigger air valve directly to the pilot chamber on the main valve. However, the performance was seriously lacking. I jsut could not dump the pilot volume nearly fast enough. So, I added the 1/2 inch bore pilot valve. Holy cow, that made a HUGE difference! I know pilotting a valve increases opening speed in most instances. That is a given. However, I had no idea it would make such a difference on a relatively small pilot volume valve. This thing rocks!

I cannot wait to setup a test rig with the 6 foot barrel and break out the chrony.

i like the look on your 2" in cannon, if i was you i would make a "little brother" to it, just scale it smaller but stilla large enough to shoot comfy. with 1" barrel you dont need so large air tank so it will be faster to reload

I have a 400 psi compressor coming and I was wondering if someone here could run the numbers on this for me.

My gun is a 1/2 inch pipe barrel, three feet long. The valve has a CV of 14. The tank to barrel ratio is 3 to 1. The PSI is 400 and there will be two different weight slugs I will be firing, 8 gram plastic slug or a 20 gram metal slug.